Patent GB-166195-A (GB)
Title: Improvements in methods and systems for the transmission of radiant energy
IPC: H04B7/12
Filed: 1918-09-26
Abstract: 166,195. Imray, O., (Hammond, J. H.). Sept. 26, 1918. Oscillation generators; secret and selective signalling systems; keying systems and apparatus; heterodyne receiving systems; thermionic amplifiers and detectors. In a system of wireless signalling, the signals are caused to vary the ultraaudible group-frequency of trains of damped waves continuously emitted from the transmitting station, or to vary the amplitude-pulsation frequency if continuous waves are employed. For secret working, the signalling group frequency may be changed from time to time by means of a continuously-rotating commutator or by a hand-operated switch. At the receiving-station, the incoming waves are rectified and are then combined with oscillations produced locally of a frequency differing slightly from the group frequency used for signalling, thereby producing audible beats. When two signalling group-frequencies are employed, two sources of oscillations are provided at the receiving station, each beating with one of the group-frequencies to produce the same audible note. Transmitting apparatus with stationary sparkgap oscillation generator. In the apparatus shown in Fig. 1, the direct-current generator 50 is connected across a condenser 22 placed in an oscillation circuit comprising a spark-gap 21 and an inductance 16. The discharge frequency is determined by a shunt across the condenser 22 comprising an inductance 40 and three condensers 41, 45, 46, of which the condenser 41 is permanently in circuit, condenser 45 is connected and disconnected by the signal key 49, and condenser 46 is connected and disconnected by a rotary commutator or by a hand switch operated from time to time. The carrier oscillations may be of a frequency of 1,000,000 and their group frequency during the spaces or intervals between the signal elements may be 32,000 or 30,000 according as the commutator is open or closed. When the key 49 is closed the group frequency may be 31,000 or 29,000 according as the commutator is open or closed. Instead of placing the auxiliary condensers 45, 46 in parallel with the main condenser 41, one or both of them may be placed in series, the switches then acting as short circuits. The commutator may have its conducting-segme.nts of such lengths and so spaced apart as to form two sets of dots " and " dashes." When the sending-key 49 is not in action these " dots " and " dashes " will be sent out as waves of frequency 1,000,000 with group frequencies alternately 32,000 and 30,000. This device is used to mislead any operator who attempts to listen in. In another arrangement, shown in Fig. 21, a thermionic generator is utilized for charging a condenser at a frequency of about 30,000, the condenser discharging through a gap and producing oscillations of, say, 1,000,000 frequency. The thermionic generator 810 has its grid and plate circuits inductively coupled, the plate circuit including an oscillatory circuit 830 having an auxiliary capacity 834 is series with the main capacity 833. This circuit is coupled to the grid circuit of a pair of rectifying valves 840 connected in parallel and arranged to produce unidirectional current impulses in the plate circuit 870 which are utilized to charge the condenser 871. The grids 843 are given a suitable negative potential by the battery 862. An inductance 876 and spark-gap 877 are connected across the condenser 871 which on discharging through the gap produces oscillations at a wave frequency determined by the circuit 875 and at a group frequency determined by the circuit 830. Signals are produced by the key 835 which, when depressed, short-circuits the auxiliary condenser 834 and thus decreases the natural frequency of the circuit 830. The spark-gap circuit 875 may be coupled inductively to the aerial circuit 879, or an auto-transformer may be used, a series condenser being then placed in the aerial circuit between the auto-transformer and earth. The signal key 835 may be arranged to short-circuit part of the inductance of the circuit 830, and for telephony a microphone may replace the signal key. In a further modification of Fig. 21, the coil 861 is omitted and the coil 831 connected at its upper end through a condenser to the grids 843, the grid potential being maintained by a battery placed between the grids 843 and filaments 844, with an iron-core inductance in series. The rectifying valves 840 may be omitted, the condenser 871 being connected directly across the inductance 861. In this case, two discharges occur at the gap 877 for each complete oscillation transferred from the generator 810. Transmitting apparatus with rotating spark-gap oscillation generators. In the modified apparatus shown in Fig. 4, the group frequencies are determined by four rotary spark discs 97 - - 100 having different numbers of sparking electrodes and all mounted on a common shaft 95. The fixed electrodes 105 - - 108 are connected to brushes bearing on the make and break segments of a commutator 120. The intermediate continuous rings of the commutator are connected by brushes to back and front contacts of a signalling- key 150. When the key is not depressed, the oscillatory circuit 81, 86 includes alternately the rotary discs 97, 98 which give group frequencies of, say, 32,000 and 30,000. When the key is depressed, the circuit includes the discs 99, 100 which give group frequencies of, say, 31,000 and 29.000. The commutator segments may be arranged to send out " dots " and " dashes" for the purpose of hindering listening in, or the commutator may be replaced by a double-pole switch operated manually from time to time. Transmitting-apparatus with thermionic oscillation generators. The grid-filament circuit of the high-frequency generator tube 210, Fig. 6, includes a portion of the aerial inductance 202, the other portion of which is in the filament-plate circuit. The amplitude of the oscillations produced is varied at an intermediate frequency by the coil 226 which is coupled to a coil 242 in the circuits of a second thermionic generator 250. The intermediate or amplitude-pulsation frequency is determined by the circuit comprised by the inductance 242, the main condenser 243 and two auxiliary condensers 265, 270, the two latter being controlled respectively by a signalling-key 266 and a commutator 271, as in the arrangement shown in Fig. 1. In a modified arrangement, shown in Fig. 13, the grid circuit of the highfrequency generator 420 includes an inductance 435 coupled to the aerial inductance 403 in the plate circuit. The aerial circuit also includes a direct current generator 405 shunted by a condenser 406, and an oscillation circuit 404 of variable frequency coupled to the grid circuit of a thermionic generator 421. The amplitude-pulsation frequency is varied as described above by connecting and disconnecting the auxiliary condensers 412, 413. Receiving-apparatus. In the apparatus shown in Fig. 8, the aerial circuit 300 and the secondary circuit 307 are tuned to the wave frequency, and the latter circuit is connected on the one hand to the filament, and on the other hand through a condenser 309 to the grid of a detector 310, the plate circuit of which includes a double circuit 327, 330 tuned to the two signalling group frequencies. These circuits are coupled to two similar circuits 336, 338 connected to the grid and filament of a vacuum tube 341. A vacuum tube 350 arranged to generate oscillations has a doubly-tuned circuit 346, 401 connected across its plate and grid, the filament having a tap connection to the common inductance 347. The two series of oscillations generated differ by the same audible frequency from the signalling group frequencies, and are transferred to the circuits 336, 338 through a condenser 365 and tap connection 367. The oscillations combine to produce audible beats in the output circuit 377, the beats being amplified bv the tube 385 and heard in the receiver 387. The local oscillator may be coupled to the receiving circuits by a connection from the condenser 365 to a point between the condenser 340 and the grid. The local oscillator may generate at a single frequency which is the mean between the two signalling group frequencies and therefore beats with both at the same audible frequency. Two separate local oscillators may be used instead of the doubly-tuned circuit 346, 401. The doubly-tuned circuits of the receiving-apparatus may be replaced by two tuned circuits 352, 353, Fig. 12, placed in series in the plate circuit of the detector 310 and tuned to the respective signalling group frequencies. Two similar circuits are arranged in the grid circuit of the tube 341, and connections are made from the local oscillators through condensers 365 and a tap connection 366 to one of the inductances. Fig. 18 shows another receiving arrangement, in which a double group frequency is employed. The plate circuit 706 of the detector 705 comprises two inductance coils 707, 708 shunted by a condenser 711, and a reaction coil 709. Coupled to the inductance 707, 708 are two circuits 717, 718 tuned to the respective group frequencies, and connected in series with a condenser 720 in the gridfilament circuit of an amplifier 725. The plate circuit of this amplifier comprises two inductance coils 727, 728 coupled respectively to the grid circuits of two generators 740, 741 which generate oscillations of a frequency differing by an equal amount from the respective group frequencies. The plate circuits of these generators include the primary coils 745, 746 of an iron-cored transformer, shunted by condensers 751, 752. The secondary coil 756 forms part of a circuit 757 tuned to the beat frequency and connected to the grid of an amplifier 760 having a. telephone 762 in the plate circuit. The amplifier 725 may be omitted, the coils 707, 708 being coupled to the grid circuits of the generators 740, 741; or a pair of circuits tuned to t